In the U.S. today approximately 1 million patients are receiving supplemental oxygen therapy through the Medicare payment system at a cost of approximately 2 billion dollars with this cost increasing annually at a rate of approximately 13% (“Long-term supplemental oxygen therapy.” Up-to-Date; Jan. 18, 2013. Brian L Tiep, MD Rick Carter, PhD, MBA).
Most of the patients receiving long term supplemental oxygen therapy (LTOT) suffer from chronic hypoxemia as a result of having a chronic obstructive pulmonary disease (COPD). Presently there is no cure for this condition. However the detrimental impact of chronic hypoxemia may be mitigated by the administration of long term oxygen therapy (LTOT). The continuous inhalation of low flows of oxygen, typically 2-3 lpm (liter per minute), from a nasal cannula increases the concentration of oxygen that the patient is breathing. It is estimated that for each 1 lpm flow, the overall inhaled concentration rises by 3-4%. The increase in oxygen concentration compensates for the poor function of the patient's lungs in absorbing oxygen.
Generally when a patient is diagnosed with chronic hypoxemia, oxygen is prescribed at a fixed flow rate based on a 20-minute titration test in the doctor's office. During the test, the patient's blood oxygen saturation is measured by either using an invasive blood gas analyzer or a non-invasive device such as a pulse oximeter. While measuring the blood saturation (SpO2), the patient may be asked to walk on a treadmill so as to measure his or her need for supplemental oxygen while exerting him or herself. Based on this brief test, a fixed flow of oxygen is prescribed. The patient may be advised to increase the flow rate of oxygen during exertion, for example, while climbing stairs, while sleeping or if they feel short of breath. The patient will need confirmation of the adequacy of oxygen treatment, with the goal of keeping the patient's oxygen saturation above 90% during all of their activities, including during sleep. Some patients may be prescribed oxygen to breathe 24 hours per day or may only require oxygen while ambulating or may need oxygen treatment only when sleeping. Among patients requiring LTOT during their waking hours, often higher flow rates are required while sleeping. It is common practice to increase the flow rate by 1 liter per min while a patient is sleeping.
If a patient needs to breathe oxygen even while resting, he or she will be given a stationary oxygen generating unit in his or her home which can be set to produce, e.g., up to 5 lpm of 93% oxygen. Generally, the units today are manually set to a prescribed flow rate in liters per minute. If a patient requires oxygen while ambulating, he or she typically will carry small high pressure oxygen cylinders or small refillable liquid oxygen dewars. Small portable oxygen generators are also available which can produce up to 3 liters per minute of continuous oxygen or deliver pulsed oxygen at higher flow rates. These portable oxygen delivery systems all have drawbacks. Portable concentrators are usually bulkier and noisier and have a relatively short battery life. The small high pressure oxygen cylinders have restricted capacity, especially the smaller ones, but do not need a battery or make the kind of noise produced by the concentrators.
Due to the expense of providing oxygen in small cylinders and dewars for ambulation, various oxygen conserving devices have been developed to conserve the oxygen flow. These prior art oxygen conserving devices only deliver short pulses of oxygen at the beginning of a patient's inhalation. By not delivering oxygen during exhalation or the later period of inhalation, the oxygen which would have had no impact on increasing the patient's oxygen saturation is conserved. There now exists both pneumatic and electronic oxygen conserving devices which claim to achieve oxygen conserving ratios from 2:1 to 7:1 compared to the delivery of continuous oxygen flow. The higher conservation ratios are achieved by the electronic devices which are programmed to skip breaths so that oxygen pulse is only delivered every other breath. However, electronic devices cannot be used on all ambulating patients since their high conservation ratios can actually result in poor oxygen saturation for the patient particularly during periods of increased oxygen utilization as in walking vigorously or walking up stairs.
Moreover, currently available conserving devices measure a drop in nasal air pressure, which for most patients is inadequate to trigger the release of oxygen under various circumstances, including: extremely reduced respiratory function; most mouth breathing; talking while walking; while walking briskly or while talking intensely; or while sleeping. Upon initiation of these ambulatory devices, patients are “taught” to focus on nasal breathing to help trigger the device. Often a patient needs to stop his or her activity and focus on his or her nasal breathing, or to put the nasal cannula probe in his or her mouth to more effectively trigger the device.
Pressure sensing of the onset of inhalation in electronic oxygen conservers is currently accomplished in one of two ways:                1. Some prior art designs employ a dual lumen cannula in which one of the lumens is dedicated to pressure sensing while the other is dedicated to the supply of oxygen. This design is meant to be more sensitive to the onset of inhalation but suffers from the drawback of only being able to deliver oxygen to one of the nasal passages.        2. Other designs use a single lumen cannula that typically has a pressure sensor connected to a T piece below the two nasal prongs. Overall pressure drop associated from inhalation is sensed from both nasal passages and oxygen is then delivered to both nasal passages.        
Both designs suffer from the drawback that if one of the patient's nasal passages is blocked, it will interfere with the detection and delivery of oxygen.
Another flaw with current oxygen generating systems is the fact that a patient's ideal need for oxygen varies with time both in the short term as a result of varying exertion and in the long term as a result of improvement or deterioration in health. When a doctor prescribes a fixed flow rate of oxygen for a patient, the doctor is mainly concerned with ensuring that the patient's blood saturation does not drop below an oxygen saturation of 88-89%. The doctor does not want to have a patient experience desaturation of oxygen below 90% during any of the patient's activities. Although there exist theoretical concerns about potential toxicities in patients administered oxygen in high concentrations (above 50 percent) for extended time periods (e.g., absorptive atelectasis, increased oxidative stress, and inflammation), clinical experience has provided little support for these concerns in the setting of LTOT. (“Long-term supplemental oxygen therapy.” Up-to-Date; Jan. 18, 2013. Brian L Tiep, MD Rick Carter, PhD, MBA).
Current oxygen treatment plans are prone to error as proved by a study by Fussell et al. (Respiratory Care. February 2003, Vol. 48 No. 2). In that study, blood saturation levels of 20 patients suffering from COPD were monitored continuously using pulse oximetry to confirm if each patient's oxygen prescription adequately maintained his or her saturation. The conclusion of the study was that there was a poor relationship between conventional oxygenation assessment methods and continuous ambulatory oximetry during LTOT screening with COPD patients. More recently in an article entitled “Critical Comparisons of the Clinical Performance of Oxygen-conserving Devices,” Am. J. Respir. Crit. Care Med. 2010 May 15; 181(10): 1061-1071, the current collection of conserving devices all based on pressure sensing were criticized as failing to deliver on their efficacy claims. The authors claimed that “Although each device activated during nose and mouth breathing, none consistently performed according to engineering expectations.”
When a patient obtains low oxygen saturation results while using conserving devices or fixed oxygen flow rates, the natural response is to simply increase the flow rate. Increased nasal flow rates become increasingly expensive and are generally not well tolerated. Some COPD patients who use stationary oxygen concentrators in their homes are financially impaired and are concerned about the power costs of continuously running an oxygen concentrator. In many cases this has led to a compliance issue where the patient may elect to not switch on the concentrator and follow the therapy as prescribed by the doctor in order to save on their electricity bill. Moreover, these oxygen concentrators throw a fair amount of heat into the room, which may further add to energy costs, i.e., for cooling the room. Current oxygen concentrator designs typically will produce a maximum flow rate, e.g., of 5 lpm. If a patient's resting prescription is 2 lpm, the patient may set a flow rate through their cannula to the required flow and the excess oxygen that is being produced is simply pushed into the nostrils which while mouth breathing may be wasted. Many oxygen therapy patients can spend a significant amount of their time while active, or talking, or napping, or sleeping with blood oxygen saturation levels that are unacceptable.
Certainly pressure-based oxygen conserving units fail to live up to their claims when mouth breathing during more vigorous activity, while talking, while eating and/or when sleeping. Often patients on ambulatory oxygen will have to stop and focus on their nose breathing, or put the nasal cannula prongs in their mouth and suck on them to trigger the release of oxygen. When oxygen needs are not being met, the simple solution is to increase the nasal flow rate, which causes increasing problems of uncomfortable nasal passage drying and sometimes nasal mucosal bleeding. Further, patients often stop their oxygen delivery system altogether when eating.
It is therefore an object of the present invention to provide a new and improved type of conserving oxygen regulator which can be used to efficiently and effectively oxygenate a patient that overcomes the aforesaid and other disadvantages of the prior art. Another object of the invention is to provide a new and improved type of conserving oxygen regulator that can be used as a standalone regulator or “piggyback” onto non-conserving regulators to make them efficient. Yet other objects of the invention are to provide a new and improved type of conserving oxygen regulator that can be incorporated in all currently used conserving oxygen generators and can be applied to multiuser hospital or clinic liquid oxygen systems to add efficiency. This invention can also allow for pulse oxygen use during sleep apnea treatment with C-PAP or Bi-PAP machines.